The County Health Rankings show us that where we live matters to our health. The health of a community depends on many different factors - ranging from health behaviors, education and jobs, to quality of health care, to the environment.

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Diet and Exercise

What Is It?

Obesity rates have continued to increase in recent years across all age groups, sexes, races, educational levels, and smoking levels.[1] While genetic factors play a contributing role, they cannot fully explain the rapid increase in obesity rates.[2] In addition to genetic factors, unhealthy diet and lack of exercise are key contributors to rising obesity rates.[2,3] Unlike genetic factors, diet and exercise can be affected by interventions at the individual and community levels. Because data on dietary and physical activity patterns are difficult to obtain, the County Health Rankings reports the percent of the adult population that is obese in an effort to capture the prevalence of low physical activity and poor diet.

Why Do We Measure It?

Often, overweight and obesity are the result of an overall energy imbalance due to both eating too many calories and getting too little physical activity.[4] The Rankings measures obesity because it is an issue that can be addressed within communities by changing unhealthy environmental conditions that contribute to poor diet and exercise.

The effects of obesity are seen in a number of contexts. Being overweight or obese increases the risk for a number of health conditions: coronary heart disease, type 2 diabetes, cancer, hypertension, dyslipidemia, stroke, liver and gallbladder disease, sleep apnea and respiratory problems, osteoarthritis, gynecological problems (infertility and abnormal menses), and poor health status.[1,4] Additionally, there are direct and indirect economic costs associated with obesity. In 1998, the U.S. spent 9.1% of total medical expenses on obesity- and overweight-associated medical costs.[5]

Measurement Strategies

A person’s body mass index (BMI) is a common method for measuring obesity. The standard threshold for obesity is defined as greater than or equal to 30 kg/sq m (weight in kilograms divided by height in meters squared). 

In addition to BMI, multiple other measures can be used for assessing obesity. The National Heart, Lung and Blood Institute guidelines recommend looking at the waist circumference of individuals because fat primarily located in the abdominal area is a risk factor for many obesity-related diseases.[4] Another method to assess the degree of obesity is to tally the number of co-morbidities an individual has for diseases associated with obesity, for example: high blood pressure, type 2 diabetes, and limited mobility.[4]

What Is the County Health Rankings Measurement Strategy?

The County Health Rankings’ measure of diet and exercise is based on county-level estimates of obesity, i.e., the percent of the adult population that has a body mass index greater than or equal to 30. The data are from the National Center for Chronic Disease Prevention and Health Promotion (NCCDPHP) in the Centers from Disease Control and Prevention.  NCCDPHP develops modeled estimates of county-level obesity rates using data from the Behavioral Risk Factor Surveillance System (BRFSS), a national, random-digit dial telephone survey. BRFSS data are representative of the adult (age 18+) non-institutionalized population living in households with a land-line telephone.[6] 

Measure Strengths & Limitations

The reliability and validity of measures of height and weight derived from self-reported data has been analyzed at great length in the context of BRFSS data and through other sources of BMI data.[7] The BRFSS measures of  weight and BMI have very high reliability (repeatability) scores.[7] Another important finding is that there are no differences in reporting based on the ethnicity of the respondent.[7] Therefore, the self-reported weight and BMI data is representative across different subsets of the population. In addition to high reliability scores, BRFSS measures of self-reported weight and BMI has high validity. The studies found the correlation between self-reports and measured weights to be very high.[7-11]

Though the reliability and validity of the BRFSS measures of weight and BMI are high, an analysis found that BRFSS data generally underestimates the obese population compared with studies that directly measured height and weight.[7]  One study discovered that both sexes under-reported high values and over-reported low values.[8] Another study found systematic under-reporting in 1.3% of men and 1.7% of women; under-reporting was related to weight, height, and whether the participant was in a weight reduction program.[11]

Ideally, rather than measuring obesity rates, the underlying interest is in measures of diet and exercise but these are difficult to measure because eating is an essential component of life (unlike smoking cigarettes, for example) and the types and intensity of exercise vary greatly. Additionally, contributors to obesity are complex and come from multiple levels: genes, metabolism, behavior, environment, culture, education, and socioeconomic status.[2]

Another limitation of the data is that the body fat percentages and conversion to BMI do not take into account the ethnicity of the respondents. Different ethnic groups have different body fat percentages and weight distributions. Therefore having BMI cut-off points that do not take into account various ethnicities will change the obesity prevalence data.[12]

A final limitation of the data is that it does not include data on childhood obesity, which would provide a more comprehensive measure of future health risk by county.

 

References

[1] Mokdad AH, Ford ES, Bowman BA, et al. Prevalence of obesity, diabetes, and obesity-related health risk factors, 2001. JAMA.2003;289:76-79
[2] Centers for Disease Control and Prevention. Overweight and obesity: Causes and consequences. Centers for Disease Control and Prevention Web Site. www.cdc.gov/obesity/causes/index.html. Updated December 7, 2009. Accessed December 17, 2009.
[3] Hensrud DD. Diet and obesity. Curr Opin Gastroenterol. 2004;20:119-124.
[4] Centers for Disease Control and Prevention. Overweight and obesity: Health consequences. Centers for Disease Control and Prevention Web Site. www.cdc.gov/obesity/causes/health.html. Updated August 19, 2009. Accessed December 16, 2009.
[5] Finkelstein EA, Fiebelkorn IC, Wang G. National medical spending attributable to overweight and obesity: How much, and who's paying? Health Aff. 2003;3:219-226.
[6] Centers for Disease Control and Prevention. Health risks in the United States: Behavioral Risk Factor Surveillance System at a glance, 2009. Centers for Disease Control and Prevention Web Site. www.cdc.gov/nccdphp/publications/aag/brfss.htm. Updated December 17, 2009. Accessed January 26, 2010.
[7] Nelson DE, Holtzman D, Bolen J, Stanwyck CA, Mack KA. Reliability and validity of measures from the Behavioral Risk Factor Surveillance System (BRFSS). Soz Praventivmed. 2001;46:S3-S42.
[8] Kuskowskawolk A, Bergstrom R, Bostrom G. Relationship between questionnaire data and medical records of height, weight and body-mass index. Int J Obes. 1992;16:1-9.
[9] Stewart AL. The reliability and validity of self-reported weight and height. J Chronic Dis. 1982;35:295-309.
[10] Stunkard AJ, Albaum JM. The accuracy of self-reported weights. Am J Clin Nutr. 1981;34:1593-1599.
[11] Jeffery RW. Bias in reported body weight as a function of education, occupation, health and weight concern. Addict Behav. 1996;21:217-222.
[12] Deurenberg P, Yap M. The assessment of obesity: Methods for measuring body fat and global prevalence of obesity. Best Pract Res Clin Endocrinol Metab. 1999;13:1-11.